Appropriate regulation of cell cycle progression is central to maintaining homeostasis in biological systems. In eukaryotes cell cycle regulation is exerted largely through a family of protein kinases known collectively as the cyclin dependent kinases or CDKs and their regulatory subunits, the cyclins. In the budding yeast, cell cycle progression is characterized, in part, by the sequential accumulation of distinct classes of cyclins which interact with a single CDK to provide the relevant inductive activity for that cell cycle interval. This research proposal is directed at understanding the regulation of one such class, the G1 cyclins. The budding yeast G1 cyclins consist of a family of proteins that are essential, rate-limiting activators of cell cycle initiation at Start. Consequently, regulation of their accumulation and activity is essential for maintaining appropriate timing of cell cycle initiation as well as for the ability to respond properly to environmental and physiological stimuli that regulate cell cycle progression. The CLN1 and CLN2 genes, which encode two of the G1 cyclins, are regulated primarily at the level of transcription initiation with peak expression occuring at the time of their required function. Transcriptional regulation oc CLN2 is conferred by two regulatory region called UAS1 and UAS2. Both are competent to confer cell cycle regulation to a heterologous reporter gene. The specific aims of this proposal are: 1) To determine the physiological role of the CLN2 transcriptional regulatory regions, UAS1 and UAS2, in cell cycle regulation through genetic and physiological studies, 2) To define the minimal UAS2 element and identify trans-acting factors required for its activity using biochemical and genetic approaches, 3) To characterize the state of trans- acting factors of UAS1 and UAS2 and their interaction with the CLN2 promoter with respect to transcriptional activation of CLN2. This aim will be accomplished through application of both biochemical and genetic approaches. Accomplishment of these Specific Aims will provide us with a more thorough understanding of the mechanisms governing activation of G1 cyclin gene expression and as a result the regulation of cell cycle initiation in yeast. We anticipate that this knowledge will be applicable to the study of cell cycle regulated gene expression and cell cycle control in animal cells. The basis for this prediction is provided by the existence of analogous genes in mammalian systems and the demonstration that inappropriate expression is associated with defects in organismal development and with malignancy.